1. Field of the Invention
The invention generally relates to shaped charges of explosive material. More particularly, the invention relates to shaped charges designed primarily for perforating subterranean well casings and formations.
2. Description of Related Art
In the normal course of completing a subterranean well for the production of valuable fluids and/or minerals, a steel pipe casing is secured within the raw well borehole by a surrounding annulus of cement. Along the length of the casing, within the desired geologic production zone, the casing, the cement annulus and the production zone formation are perforated to provide fluid flow channels from the formation structure into the casing bore.
There are many variations to this theme which also includes open-hole and sand pack completions wherein there is no casing along the production zone in need of perforation. In any case, the formation zone is artificially fractured to induce drainage of fluid trapped within the formation interstices. Although there are several method options for well perforation, explosive perforation by means of shaped charges may be the most widely used.
A shaped charge is a relatively small module of highly explosive material that is encapsulated and geometrically configured to release a substantially linear plasma or jet of high temperature energy upon detonation. A plurality of these modules are secured within an elongated, generally cylindrical perforating “gun”. The charges are usually distributed along the length of the gun and aligned to discharge radially outward from the cylinder axis along a substantially radial discharge axis.
In general, a shaped charge comprises a cup-like outer case of high strength material such as steel to serve as a containment vessel for focusing the energy discharge along a line emanating from the case. The explosive material is formed within the case. The outer surface of the explosive material is formed to a normal axis concavity and the concavity faced or clad with a “liner”. Usually the liner is a thin section of relatively heavy metal such as brass, copper, lead etc, As the ignited explosive decomposes around the concavity, the liner material is radially compressed by immense pressure to be ejected as a fluidized plasma along the cavity axis of revolution.
The geometry of this concavity and properties of the liner are critical to the penetration performance of the shaped charge. Accordingly, an object of the present invention is a shaped charge having substantially improved efficiency, material penetration depth and hole diameter.